The central unit in a modular camera system consists of a camera body which can be combined with a large number of accessories of different types, for example lenses, flash units and magazines of various types. These accessories must be able to be attached and removed in principle at any time, irrespective of the state of other attached components in the system. In the camera body there is a control unit for controlling the camera body and attached accessories, which control unit requires information regarding which different types of accessory are attached in order to be able to control the system correctly. It is therefore important that this control unit receives information in a quick and reliable way regarding which accessories are attached and, of course, also if a particular accessory is removed.
If an accessory is attached when the camera system is switched off or in an energy-saving mode it is also important that the exchange of information between this accessory and the camera's central control unit is carried out as soon as the accessory has been attached. If the exchange of information between the camera's central control unit and the newly-attached accessory has to wait until the photographer switches the camera on, this can delay his ability to use the camera at the required time. In the same way, it is, of course, important that the control unit receives information that a particular accessory has been removed, irrespective of whether this is carried out while the camera is switched on, switched off or in energy-saving mode.